The present invention relates generally to a system for preventing backflow of fluid along a tube, and particularly to a system for preventing backflow of liquid in a tube used to protect signal transfer lines, such as those containing electric cable and/or optic fiber, in a downhole, wellbore environment.
A variety of tools are used at subsurface locations from which or to which a variety of output signals or control signals are sent. For example, many subterranean wells are equipped with tools or instruments that utilize electric and/or optical signals, e.g. pressure and temperature gauges, flow meters, flow control valves, and other tools. (In general, tools are any device or devices deployed downhole which utilize electric or optical signals.) Some tools, for example, may be controlled from the surface by an electric cable or optical fiber. Similarly, some of the devices are designed to output a signal that is transmitted to the surface via the electric cable or optical fiber.
The signal transmission line, e.g. electric cable or optical fiber, is encased in a tube, such as a one quarter inch stainless steel tube. The connection between the signal transmission line and the tool is accomplished in an atmospheric chamber via a connector. Typically, a metal seal is used to prevent the flow of wellbore fluid into the tube at the connector. This seal is obtained by compressing, for example, a stainless steel ferrule over the tube to form a conventional metal seal.
However, the hostile conditions of the wellbore environment render the connection prone to leakage. Because the inside of the connector and tube may stay at atmospheric pressure while the outside pressure can reach 15,000 PSI at high temperature, any leak results in the flow of wellbore fluid into the tube. The inflow of fluid invades the internal connector chamber and interior of the tube, resulting in a failure due to short circuiting of the electric wires or poor light transmission through the optic fibers. This, of course, effectively terminates the usefulness of the downhole tool.
It would be advantageous to have a system for preventing the backflow of wellbore fluids along the protective tube (or other types of tubes) from one wellbore zone to another.
The present invention provides a technique for preventing backflow of fluid, such as wellbore fluid, along a tube. The technique further allows for the use of signal transmission lines deployed in the interior of a tube, such as a stainless steel tube, extending to a subsurface location, e.g. a downhole location within a wellbore. Thus, signals can be transmitted from one zone to another while being protected by the outer tube. However, wellbore fluids are prevented from crossing from one zone to another in the event such fluid enters the tube. The technique includes the use of a penetrator combined with a zone separation device, such as a feed-through packer, a tubing hanger or an annulus safety valve. The system, however, should not be limited to any particular zone separation devices or tubes.